The present invention relates to a method of drawing a pattern on a base material by scanning a beam, and a pattern drawing apparatus using an electron beam, and in particular, to those which can draw a microscopic pattern.
In recent years, in the field of optical pickup devices, which has developed quickly, used are optical elements such as an extremely precise objective lens and the like. By molding the optical elements from a material such as a plastic or glass with metal molding dies, it is possible to quickly produce uniform products, and accordingly it can be said that metal molds are suitable for mass production. Generally, the metal molding dies are mainly manufactured, being cut section by section, with monocrystal diamond tools. However, such metal molding dies are consumable items which are worn away based on the number of usage, and it is necessary to exchange the metal molding dies periodically. Accordingly, an identical metal molding die must be prepared for the exchange, however, when such metal molding dies are manufactured by cutting conducted with monocrystal diamond tools, it is very difficult to cut the identical metal molding dies, and further, there is the problem that the form of the optical element products vary widely before and after the exchange, and in addition, it is very expensive, which is another problem.
To overcome these problems, there is a trial to form the metal molding dies in such a way that electroforming is allowed to grow on the basic configuration having the base optical surface corresponding to the optical surface of the optical element. According to the trial, however microscopic a pattern formed on the base optical surface of the basic configuration may be, it is possible to mold the pattern with high precision.
The pattern of the basic configuration used for the above-mentioned usage can be produced in such a way that a resist is coated on the base optical surface of a base material as an object of pattern drawing (hereinafter referred to as a base material), a microscopic pattern is formed by pattern drawing using an electro beam, the resist is developed, and the pattern can be produced by a dry etching method. After the basic configuration is adhered onto a jig, the electroforming is grown so as to cover the base optical surface of the basic configuration, and an electroforming member, as the desired metal molding die, is formed.
Originally, since the pattern drawing using the electro beam is one which forms the microscopic pattern, the beam scanning area (pattern-drawn field on which a pattern is drawn by scanning a beam) for one operation is 0.5×0.5 mm, which is an extremely small area. On the other hand, an optical element such as an objective lens for the optical pickup device is about 3 mm diameter, and the base optical surface of the base material is sized depending on the optical element, and thereby, it is not possible to form the microscopic pattern on the base optical surface of the base material in one operation. Due to this, a drawing method has been devised in which after the drawing is completed in one scanning area of the electro beam, an electro beam emitting source and the base material are relatively shifted to an adjacent scanning area, and the drawing is continued there. This is called a step and repeat method.
When a pattern that is drawn in one scanning area is to be continuous with a pattern drawn in the adjacent scanning area, the problem is how to precisely draw bordering sections. Regarding the drawing of such continuous patterns, dose quantity of the electron beam (this is shown by an electron radiating amount for one unit area) should be nearly equal, from the bordering section of a preceding pattern that is drawn in the one scanning area, to the succeeding pattern drawn in the adjacent scanning area, where it touches the bordering section of the preceding pattern. Even if the dose quantity of the electron beam were established as mentioned above, the electron beam has characteristics in that radiating direction changes with temperature, magnetic field, and vibration. When the drawing is conducted, such drawbacks can be happened that the bordering section of the preceding pattern is overlapped by the bordering section of the succeeding pattern, or the bordering section of the preceding pattern is separated from the bordering section of the succeeding pattern. In case of the former drawback, the dose quantity becomes excessive in the bordering section, and in case of the latter drawback, the dose quantity becomes extremely small in the bordering section, and whichever may happen, the patterns will not be continuous, which influences formation of the ring-shaped diffractive zone shaped to be ideal. (FIGS. 1(A) and 1(B), see below for further details)